Bogus base station an ill-kept secret

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The FBI's long battle to keep details of its controversial Stingray mobile phone-snooping kit under wraps has escalated, with US Marshals raiding Florida police to prevent their records being released, while a Florida judge was busily unsealing court evidence covering the IMSI-catchers.

The American Civil Liberties Union had succeeded in convincing a judge that evidence given in court should be released. So, to keep anything the police held from being released, US Marshals have reportedly confiscated documents from Sarasota Police on the basis that they're federal property.

While the evidence confirms what the tech-savvy either already knew, or had at least surmised, the unsealing of the evidence puts some of Stingray's capabilities, as well as the uses to which it's put in the US, in the public domain. That, the ACLU hopes, will mean the wiretap boxes get wider public scrutiny and debate.

The nature and use of Stingray came to light in cases like this one in Arizona, but the FBI and courts have resisted publishing details of the devices.

However, the ACLU had a win in Tallahassee, Florida, where a judge has unsealed police evidence given about how Stingray was used to track a suspect to an apartment.

It was already known that the Stingrays acted as a dummy mobile base station. Since mobile phones default to registering to whichever base station has the strongest signal, the device need only identify itself as the target's carrier and any nearby phones will log into it rather than a “real” base station.

When the target's phone, identified by its IMEI number, logs into Stingray, the box then tries to get a direction to the phone, and by moving around, the police can triangulate to the location.

To avoid losing the signal – and to make it easier to find targets in noisy environments – the officer giving evidence told the court Stingray “forces that handset to transmit at full power”.

In spite of a pop-culture-fed belief in the nearly omnipotent power of surveillance, Stringray turns out to be somewhat constrained. Having identified an apartment complex that the target's phone was in, the Tallahassee police had to conduct door-to-door snooping to work out which particular apartment they needed to raid.

About the US Marshal's confiscation of documents, the ACLU says: “Their explanation: the Marshals Service had deputized the local officer, and therefore the records were actually the property of the federal government.”

The ACLU has filed an emergency court motion to prevent further documents being transferred. ®